Background: Many studies have demonstrated the beneficial effect of tea on dental caries. Aim: The aim of the present study was to compare and evaluate the effect of green tea and black tea infusions on salivary pH in caries free and with caries individuals. Settings and Design: Randomized double-blinded concurrent parallel study. Materials and Methods: Forty healthy subjects, aged 18-20 years participated in the study. Commercially available green tea (Tetley Pure Green Tea) and black tea (Tetley Black Tea) were used in the study. The pH of saliva and of the tested tea products was determined with a digital pH meter. pH of whole saliva was measured at baseline and immediately after the intake of product (0), 5, and 10 min later. Data analysis was carried out by Student's t-test and repeated measure ANOVA. Results:In vitro pH determination of infusion showed pH value of green tea (6.27 ± 0.02) was higher compared to black tea (6.13 ± 0.03). Both green and black tea infusion intake led to a statistically significant rise in salivary pH, both in caries-free and with caries groups, which remained above the base salivary pH over the whole period of measurements. Conclusion: The present study demonstrated that after intake of both green and black tea there was an increase in salivary pH both in caries-free and with caries groups. The pH rise was more in green tea intake compared to black tea.

Tea is the second most widely consumed beverage in the world after water. [1] Regular intake of tea is associated with improved antioxidant status in vivo, which may contribute to lowering the risk of coronary heart disease, stroke, and certain types of cancer. [2],[3],[4],[5],[6] There are three major categories of tea: Non-fermented green tea, partially fermented oolong tea, and fully fermented black tea. [1] Considerable interest has developed in the past decade in unraveling the beneficial health effects of tea, particularly in its polyphenolic components and antioxidant activity. [2],[3] India is the largest tea consuming country, accounting for 22.5% of the total world consumption followed by China at 20.09%. Almost 85% of Indian households consume tea. Unlike international market where iced tea is prevalent, tea in India is generally consumed as a hot beverage infused either separately or as a mixture of milk and sugar. [7]

There are reports that tea consumption may decrease dental caries in humans and laboratory animals. [8],[9],[10],[11],[12],[13] Polyphenols in tea inhibit bacterial growth and ward off mouth infections. Tea is a natural source of fluoride, therefore helping to promote healthy tooth enamel. Also, tannins present in black tea inhibit the growth of plaque-causing bacteria apart from inhibiting the action of salivary amylase, thus making their contribution in cavity prevention. Magalhaes et al., [14] found that mouth rinsing with green tea extract (0.61%) protected tooth dentine from erosion and abrasion similar to mouth rinsing with fluoride extract (250 ppm) or chlorhexidine extract. Prevention of pH decrease in the vicinity of teeth enamel and blocking bacterial adhesion are additional mechanisms explaining the anti-cariogenic properties of tea. [14],[15],[16] However, little is known of the acid content of tea and its influence on salivary pH during consumption. Thus, the aim of this study was to compare and evaluate the effect of green tea and black tea infusions on salivary pH in caries-free and with caries individuals.

Materials and Methods

Forty healthy subjects, aged 18-20 years, with minimum of 20 natural permanent teeth and mean plaque score of 0-0.9 (Sillness and Loe index [17] ) participated in the study. Ethical approval for the study was received from College of Dental Sciences ethics committee (CODS/27/2011-2012), and informed consent was obtained from each subject by means of a signed form. At the first visit, number of DMFT/DMFS was recorded and subjects were divided in to two groups; caries free (DMFT/DMFS = 0) and with caries (DMFT/DMFS = one to three). Both the participants and investigator was blinded.

Forty subjects were randomly divided into four study groups with 10 participants in each group. Group A (GT): Ten caries free subjects were given green tea infusion.

Group B (GTD):

Ten with caries subjects were given green tea infusion

Group C (BT):

Ten caries free subjects were given black tea infusion

Group D (BTD):

Ten with caries subjects were given black tea infusion.

Tea products used in this study were as follows: Commercially available green tea (Tetley Pure Green Tea) and black tea (Tetley Black Tea). The preparation of green tea and black tea infusions was performed following the recommendations of the manufacturers. Each tea bag sample was added separately to 90 ml of freshly boiled water and stirred. The tea bags were taken out after 3 min.

Blinding: Infusions were prepared by another investigator, and the preparations were coded before distributing it to the participants.

On each day, at least 60 min after breakfast and 15 min after tooth cleaning (tooth brush: Oral B soft; tooth paste: Colgate Total) the pH of non-stimulated whole saliva (base value) was measured. Samples of whole saliva for each determination were taken from the sublingual region by aspiration using a sterile plastic syringe. The pH of saliva and of the tested tea products was determined with a digital pH meter (335 Systronics, India). pH meter had an accuracy of ± pH 0.01. It was calibrated each day prior to the first measurement with buffering solutions from HiMedia (Mumbai, India). A test product (30 ml) was given to each subject. Immediately after the intake of product (0), 5, and 10 min later, whole saliva was collected as described above and the pH value was measured again.

Statistical analysis

Data analysis was carried out by Student's t-test and repeated measure ANOVA. The Statistical Package for Social Science version 17 (SPSS INC., Chicago link) was used to perform the analysis. All statistical tests were two-sided, and the significance level was set at P < 0.05.

Results

0In vitro pH determination of infusion showed pH value of green tea (6.27 ± 0.02) was higher compared to black tea (6.13 ± 0.03) but the difference was not statistically significant. The mean base value of the pH of whole saliva was 6.99 ± 0.06. There were no significant differences in the levels of salivary pH in subjects with (6.88 ± 0.12) or without dental decay (6.98 ± 0.09). Green tea led immediately after intake to a statistically significant (P < 0.05) rise in salivary pH, both in caries-free and with caries group, which remained above the base salivary pH over the whole period of measurements. The black tea intake also showed rise in salivary pH in both groups but the difference was not statistically significant [Table 1]. When group A and B were combined and compared with group C and D, green tea led immediately after intake to a statistically significant (P < 0.05) rise in salivary pH compared to black tea [Table 2].

Table 1: The mean pH of whole saliva at the various times of mesurement in caries free and with caries group

There exists a growing knowledge of the importance of saliva in oral and dental health since its components and its pH are some of the factors involved in the development of caries. [18] Salivary pH indicates the hydrogen ion concentration present in the saliva solution, thus allowing a calculation of acidic oral alkaline saliva characteristics. Average pH of saliva at rest is about 6.8, and it varies between 6.5 and 7.0. In non-stimulated saliva or when flow is low, chloride is the predominant ion, and there are only traces of bicarbonate, resulting in a lower pH. The mean pH of non-stimulated whole saliva in the present study was 6.99 ± 0.06, which is comparable with the findings of previous studies. [14],[15],[19] Baseline mean salivary pH was slightly lower in subjects with caries (6.88 ± 0.12) compared to caries-free subjects (6.98 ± 0.09) but the difference was not statistically significant. This finding is in line with previous studies which showed no significant correlation between mean salivary pH values among subjects with or without caries. [20],[21] In contrast, Tayab et al., [22] showed statistically significant difference in mean pH value of saliva among subjects with and without caries.

In the present study, different salivary pH changes were observed immediately after intake of the tested green and black tea and in the period of 5, and 10 minutes, corresponding to their composition. The result showed intake of both green and black tea showed rise in salivary pH above the baseline value both in caries-free and with caries groups but the result was statistically significant in the green tea group at all time intervals. The salivary properties, bacterial composition of saliva, and residual plaque as well as type of beverages, added sugar, and their baseline pH-values influence the changes in salivary pH. Baseline mean plaque score of study participants in the present study varied from 0-0.9, and all the subjects brushed their teeth 15 min before taking the test products. Baseline pH values were slightly higher in green tea infusion compared to black tea but the difference was not statistically significant, and no sugar was added to the infusions in the present study.

The studies have shown that consumption of tea reduced caries development, [8],[9],[10],[11],[12],[13],[14],[15] and the effect is attributed to its fluoride content, [9],[10] polyphenols, [11] and catechin [12],[13],[14],[15] components. A study conducted by Hamilon-Miller [12] concluded that rinsing with green tea catechins for suitable time prevent acid production and preserve pH within normal range (7.2-7.4), which is not a favorable conditions for Streptococcus mutans growth, and he stated that green tea possess anti-cariogenic and antibacterial properties. Hirasawa et al., [13] evaluated the plaque pH value at different intervals 0, 3, 7, 11, 20, and 30 min among 15 subjects before and after rinsing with 2% green tea for 5 min; they proved that there was a significant difference among subjects concerning plaque pH values at 3, 7, and 11 min. A study conducted by Lσpez et al., [19] revealed that there were significant differences in the saliva pH levels between types of infusions, probably related to their different buffer capacity.

Conclusion

The beneficial effect of tea on general health is attributed to its flavonoids and antioxidant components. The present study demonstrated that after intake of both green and black tea, there was an increase in salivary pH both in caries-free and with caries groups. The pH rise was more in green tea intake compared to black tea. Further studies with larger sample size are required to confirm the beneficiary effects of tea on oral health.